The present invention relates generally to fluid ejection devices, and more particularly to a substrate for a fluid ejection device.
In some fluid ejection devices, such as printheads, a drop ejecting element is formed on a substrate and fluid is routed to an ejection chamber of the drop ejecting element through an opening or slot in the substrate. Often, the substrate is a silicon wafer and the slot is formed in the wafer by chemical etching. Existing chemical etching processes, however, result in etch angles that cause a very wide backside opening of the slot in the substrate. The backside of the substrate is defined as a side of the substrate opposite of which the drop ejecting element is formed.
Unfortunately, the wide backside slot opening limits how close to each other slots can be formed in a particular die. In addition, the wide backside slot opening reduces useful area of the backside of the substrate. For example, the wide backside slot opening reduces adhesion area of the backside of the substrate.
Accordingly, it is desired to minimize a size of the opening in the backside of the substrate.
One aspect of the present invention provides a method of forming an opening through a substrate. The method includes etching a first portion of the opening into the substrate from a first side, etching a plurality of second portions of the opening into the substrate from a second side opposite the first side, continued etching of at least one of the first portion and the plurality of second portions of the opening to the other of the first portion and the plurality of second portions of the opening, and overetching each of the second portions of the opening at an interface between the first portion and each of the second portions of the opening, including communicating each of the second portions with an adjacent one of the second portions.